Detection of epidermal growth factor receptor gene T790M mutation in cytology samples using the cobas® EGFR mutation test

Objective: Detection of epidermal growth factor receptor (EGFR) gene mutations is essential in deciding therapeutic strategy in non-small cell lung cancer (NSCLC) patients at initial diagnosis. Moreover, in EGFR mutation positive (EGFRm) NSCLC patients, re-biopsy at disease progression to clarify resistance mechanisms is also important. However, collecting histology samples is often difficult because of inaccessibility and invasiveness. In some cases, only cytology samples can be collected, and studies have reported that cytology samples are appropriate for EGFR gene mutation testing. The cobas (R) EGFR Mutation Test (Roche Molecular Systems Inc., Branchburg, New Jersey, USA) is approved as a companion diagnostic for osimertinib, a third-generation EGFR-tyrosine kinase inhibitor approved in Japan. However, it is not clear whether the EGFR T790M mutation can be detected in cytology samples using this test. The primary objective of this study was to assess concordance of EGFR T790M gene mutation detection between histology and matched cytology samples using the cobas (R) EGFR Mutation Test. Materials and methods: We conducted a multicenter, observational study in Japan. Overall, 41 EGFRm NSCLC patients who had both histology and cytology samples collected at the same time at re-biopsy and with the results of EGFR mutation test using histology samples were enrolled. The EGFR mutation status of both sample types was tested using the cobas (R) EGFR Mutation Test and the concordance rates were calculated. Results: The EGFR T790M mutation detection rate in histology and cytology samples was 42.5% and 37.5%, respectively. The overall percent agreement between the histology and cytology samples was 91.7%. Conclusions: These data demonstrate that the cobas (R) EGFR Mutation Test can detect the EGFR T790M mutation in both cytology and histology samples.